Treatment Fluids Comprising Vitrified Shale and Methods of Using Such Fluids in Subterranean Formations

ABSTRACT

Methods and compositions for the treatment of subterranean formations, and more specifically, treatment fluids containing vitrified shale and methods of using these treatment fluids in subterranean formations, are provided. An example of a method is a method of displacing a fluid in a well bore. Another example of a method is a method of separating fluids in a well bore in a subterranean formation. An example of a composition is a spacer fluid comprising vitrified shale and a base fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/969,570, entitled “Methods of Treating Particulates and Usein Subterranean Formations,” filed on Oct. 20, 2004, the entirety ofwhich is herein incorporated by reference.

BACKGROUND

The present invention relates to subterranean treatment operations, andmore particularly, to improved treatment fluids comprising vitrifiedshale, and methods of using these improved treatment fluids insubterranean formations.

Treatment fluids are used in a variety of operations that may beperformed in subterranean formations. As referred to herein, the term“treatment fluid” will be understood to mean any fluid that may be usedin a subterranean application in conjunction with a desired functionand/or for a desired purpose. The term “treatment fluid” does not implyany particular action by the fluid. Treatment fluids often are used in,e.g., well drilling, completion, and stimulation operations. Examples ofsuch treatment fluids include, inter alia, drilling fluids, well cleanupfluids, workover fluids, conformance fluids, gravel pack fluids,acidizing fluids, fracturing fluids, spacer fluids, and the like.

Spacer fluids often are used in oil and gas wells to facilitate improveddisplacement efficiency when displacing multiple fluids into a wellbore. For example, spacer fluids often may be placed within asubterranean formation so as to physically separate incompatible fluids.Spacer fluids also may be placed between different drilling fluidsduring drilling-fluid changeouts, or between a drilling fluid and acompletion brine.

Spacer fluids also may be used in primary cementing operations toseparate, inter alia, a drilling fluid from a cement composition thatmay be placed in an annulus between a casing string and the subterraneanformation, whether the cement composition is placed in the annulus ineither the conventional or reverse-circulation direction. The cementcomposition often is intended, inter alia, to set in the annulus,supporting and positioning the casing string, and bonding to both thecasing string and the formation to form a substantially impermeablebarrier, or cement sheath, which facilitates zonal isolation. If thespacer fluid does not adequately displace the drilling fluid from theannulus, the cement composition may fail to bond to the casing stringand/or the formation to the desired extent. In certain circumstances,spacer fluids also may be placed in subterranean formations to ensurethat all down hole surfaces are water-wetted before the subsequentplacement of a cement composition, which may enhance the bonding thatoccurs between the cement composition and the water-wetted surfaces.

Conventional treatment fluids, including spacer fluids, often comprisematerials that are costly and that, in certain circumstances, may becomeunstable at elevated temperatures. This is problematic, inter alia,because it may increase the cost of subterranean operations involvingthe treatment fluid.

SUMMARY OF THE INVENTION

The present invention relates to subterranean treatment operations, andmore particularly, to improved treatment fluids comprising vitrifiedshale, and methods of using these improved treatment fluids insubterranean formations.

An example of a method of the present invention is a method ofdisplacing a fluid in a well bore, comprising: providing a well borehaving a first fluid disposed therein; and placing a second fluid intothe well bore to at least partially displace the first fluid therefrom,wherein the second fluid comprises vitrified shale and a base fluid.

Another example of a method of the present invention is a method ofseparating fluids in a well bore in a subterranean formation,comprising: providing a well bore having a first fluid disposed therein;placing a spacer fluid in the well bore to separate the first fluid froma second fluid, the spacer fluid comprising vitrified shale and a basefluid; and placing a second fluid in the well bore.

An example of a composition of the present invention is a spacer fluidcomprising vitrified shale and a base fluid.

The features and advantages of the present invention will be readilyapparent to those skilled in the art upon a reading of the descriptionof the preferred embodiments that follows.

DETAILED DESCRIPTION

The present invention relates to subterranean treatment operations, andmore particularly, to improved treatment fluids comprising vitrifiedshale, and methods of using these improved treatment fluids insubterranean formations. The treatment fluids of the present inventionare suitable for use in a variety of subterranean treatmentapplications, including well drilling, completion, and stimulationoperations.

The treatment fluids of the present invention generally comprisevitrified shale and a base fluid. Optionally, the treatment fluids ofthe present invention may comprise additional additives as may berequired or beneficial for a particular use. For example, the treatmentfluids of the present invention may include viscosifying agents, organicpolymers, dispersants, surfactants, weighting agents, and the like.

The vitrified shale utilized in the treatment fluids of the presentinvention generally comprises any partially vitrified silica-richmaterial. Vitrified shale includes any fine-grained rock formed by theconsolidation of clay or mud that has been at least partially convertedinto a crystalline, glassy material by heat and fusion. In certainembodiments of the present invention, the vitrified shale has a percentvolume oxide content, as determined by quantitative x-ray diffraction,as set forth in Table 1 below. TABLE 1 Oxide Volume % SiO₂ 57-73 Al₂O₃15-25 Fe₂O₃ 3-7 CaO 2-6 K₂O 1-5 SO₃ 1-3 MnO, SrO, TiO₂, BaO, and each<1% Na₂OAn example of a suitable vitrified shale is commercially available underthe trade name “PRESSUR-SEAL® FINE LCM” from TXI Energy Services, Inc.,of Houston, Tex. In certain embodiments of the present invention, thevitrified shale is present in the treatment fluids of the presentinvention in an amount in the range of from about 0.01% to about 90% byweight of the treatment fluid. In other embodiments of the presentinvention, the vitrified shale is present in the treatment fluids of thepresent invention in an amount in the range of from about 1% to about20% by weight of the treatment fluid. In other embodiments of thepresent invention, the vitrified shale is present in the treatmentfluids of the present invention in an amount in the range of from about1% to about 10% by weight of the treatment fluid. One skilled in theart, with the benefit of this disclosure, will recognize a suitableamount of vitrified shale for a particular application.

The base fluid utilized in the treatment fluids of the present inventionmay comprise an aqueous-based fluid, an oil-based fluid, a syntheticfluid, or an emulsion. In certain embodiments of the present invention,the base fluid may be an aqueous-based fluid that comprises fresh water,salt water, brine, sea water, or a mixture thereof. In certainembodiments of the present invention, the base fluid may be anaqueous-based fluid that may comprise cesium and/or potassium formate.The base fluid can be from any source provided that it does not containcompounds that may adversely affect other components in the treatmentfluid. The base fluid may be from a natural or synthetic source. Incertain embodiments of the present invention, the base fluid maycomprise a synthetic fluid such as, but not limited to, esters, ethers,and olefins. Generally, the base fluid will be present in the treatmentfluids of the present invention in an amount sufficient to form apumpable slurry. In certain embodiments, the base fluid will be presentin the treatment fluids of the present invention in an amount in therange of from about 15% to about 95% by weight of the treatment fluid.In other embodiments, the base fluid will be present in the treatmentfluids of the present invention in an amount in the range of from about25% to about 85% by weight of the treatment fluid. One of ordinary skillin the art, with the benefit of this disclosure, will recognize theappropriate amount of base fluid to use for a chosen application.

Optionally, the treatment fluids of the present invention further maycomprise a viscosifying agent. The viscosifying agent may be anycomponent suitable for providing a desired degree of solids suspension.The choice of a viscosifying agent depends upon factors such as thedesired viscosity and the desired chemical compatibility with otherfluids (e.g., drilling fluids, cement compositions, and the like). Incertain embodiments of the present invention, the viscosifying agent maybe easily flocculated and filtered out of the treatment fluids of thepresent invention. Suitable viscosifying agents may include, but are notlimited to, colloidal agents (e.g., clays, polymers, guar gum), emulsionforming agents, diatomaceous earth, starches, biopolymers, syntheticpolymers, or mixtures thereof. Suitable viscosifying agents often arehydratable polymers that have one or more functional groups. Thesefunctional groups include, but are not limited to, hydroxyl groups,carboxyl groups, carboxylic acids, derivatives of carboxylic acids,sulfate groups, sulfonate groups, phosphate groups, phosphonate groups,and amino groups. In certain embodiments of the present invention,viscosifying agents may be used that comprise hydroxyl groups and/oramino groups. In certain embodiments of the present invention, theviscosifying agents may be biopolymers, and derivatives thereof, thathave one or more of these monosaccharide units: galactose, mannose,glucoside, glucose, xylose, arabinose, fructose, glucuronic acid, orpyranosyl sulfate. Examples of suitable biopolymers include, but are notlimited to, guar gum and derivatives thereof, such as hydroxypropyl guarand carboxymethyl hydroxypropyl guar, and cellulose derivatives, such ashydroxyethyl cellulose, welan gums, and xanthan gums. Additionally,synthetic polymers that contain the above-mentioned functional groupsmay be used. Examples of such synthetic polymers include, but are notlimited to, poly(acrylate), poly(methacrylate), poly(ethylene imine),poly(acrylamide), poly(vinyl alcohol), and poly(vinylpyrrolidone). Othersuitable viscosifying agents include chitosans, starches and gelatins.Suitable clays include kaolinites, montmorillonite, bentonite, hydrousmicas, attapulgite, sepiolite, and the like, as well as synthetic clays,such as laponite. An example of a suitable viscosifying agent is ahydroxyethyl cellulose that is commercially available under the tradename “WG-17” from Halliburton Energy Services, Inc., of Duncan, Okla.Another example of a suitable viscosifying agent is a welan gum that iscommercially available under the trade name “BIOZAN” from Kelco OilfieldServices, Inc. Where included, the viscosifying agent may be present inthe treatment fluids of the present invention in an amount sufficient toprovide a desired degree of solids suspension. In certain embodiments,the viscosifying agent may be present in an amount in the range fromabout 0.01% to about 35% by weight of the treatment fluid. In otherembodiments, the viscosifying agent may be present in an amount in therange from about 0.5% to about 2% by weight of the treatment fluid. Incertain embodiments of the present invention wherein the treatmentfluids will be exposed to elevated pH conditions (e.g., when thetreatment fluids will be contacted with cement compositions),viscosifying agents such as welan gum, cellulose (and cellulosederivatives), and xanthan gum may be particularly suitable. One ofordinary skill in the art, with the benefit of this disclosure, will beable to identify a suitable viscosifying agent, as well as theappropriate amount to include, for a particular application.

Optionally, the treatment fluids of the present invention further maycomprise a fluid loss control additive. Any fluid loss control additivesuitable for use in a subterranean application may be suitable for usein the compositions and methods of the present invention. In certainembodiments, the fluid loss control additive may comprise organicpolymers, starches, or fine silica. An example of a fine silica that maybe suitable is commercially available from Halliburton Energy Services,Inc. under the trade name “WAC-9.” An example of a starch that may besuitable is commercially available from Halliburton Energy Services,Inc. under the trade name “DEXTRID.” In certain embodiments where thetreatment fluids of the present invention comprise a fluid loss controladditive, the fluid loss control additive may be present in thetreatment fluids of the present invention in an amount in the range fromabout 0.01% to about 6% by weight of the treatment fluid. In otherembodiments, the fluid loss control additive may be present in thetreatment fluids of the present invention in an amount in the range fromabout 0.05% to about 0.1% by weight of the treatment fluid. One skilledin the art, with the benefit of this disclosure, will recognize theappropriate amount of a fluid loss control additive to use for aparticular application.

Optionally, the treatment fluids of the present invention may comprise adispersant. Suitable examples of dispersants include, but are notlimited to, sulfonated styrene maleic anhydride copolymer, sulfonatedvinyl toluene maleic anhydride copolymer, sodium naphthalene sulfonatecondensed with formaldehyde, sulfonated acetone condensed withformaldehyde, lignosulfonates (e.g., modified sodium lignosulfonate),allyloxybenzene sulfonate, allyl sulfonate and non-ionic monomers, andinterpolymers of acrylic acid. An example of a dispersant that may besuitable is commercially available from National Starch & ChemicalCompany of Newark, N.J. under the trade name “Alcosperse 602 ND,” and isa mixture of 6 parts sulfonated styrene maleic anhydride copolymer to3.75 parts interpolymer of acrylic acid. Another example of a dispersantthat may be suitable is a modified sodium lignosulfonate that iscommercially available from Halliburton Energy Services, Inc., ofDuncan, Okla., under the trade name “HR®-5.” Where included, thedispersant may be present in an amount in the range from about 0.0001%to about 4% by weight of the treatment fluid. In other embodiments, thedispersant may be present in an amount in the range from about 0.0003%to about 0.1% by weight of the treatment fluid. One skilled in the art,with the benefit of this disclosure, will recognize the appropriateamount of dispersant for inclusion in the treatment fluids of thepresent invention for a particular application.

Optionally, the treatment fluids of the present invention may comprisesurfactants. Suitable examples of surfactants include, but are notlimited to, nonylphenol ethoxylates, alcohol ethoxylates, sugar lipids,α-olefinsulfonates, alkylpolyglycosides, alcohol sulfates, salts ofethoxylated alcohol sulfates, alkyl amidopropyl dimethylamine oxides,and alkene amidopropyl dimethylamine oxides. An example of a surfactantthat may be suitable comprises an oxyalkylatedsulfonate, and iscommercially available from Halliburton Energy Services, Inc. under thetrade name “STABILIZER 434C.” Another surfactant that may be suitablecomprises an alkylpolysaccharide, and is commercially available fromSeppic, Inc. of Fairfield, N.J. under the trade designation“SIMUSOL-10.” Another surfactant that may be suitable comprisesethoxylated nonylphenols, and is commercially available under the tradename “DUAL SPACER SURFACTANT A” from Halliburton Energy Services, Inc.Where included, the surfactant may be present in an amount in the rangefrom about 0.01% to about 10% by weight of the treatment fluid. In otherembodiments of the present invention, the surfactant may be present inan amount in the range from about 0.01% to about 6% by weight of thetreatment fluid. One skilled in the art, with the benefit of thisdisclosure will recognize the appropriate amount of surfactant for aparticular application.

Optionally, the treatment fluids of the present invention may compriseweighting agents. Generally, any weighting agent may be used with thetreatment fluids of the present invention. Suitable weighting materialsmay include barium sulfate, hematite, manganese tetraoxide, ilmenite,calcium carbonate, and the like. An example of a suitable hematite iscommercially available under the trade name “Hi-Dense® No. 4” fromHalliburton Energy Services, Inc. Where included, the weighting agentmay be present in the treatment fluid in an amount sufficient to providea desired density to the treatment fluid. In certain embodiments, theweighting agent may be present in the treatment fluids of the presentinvention in the range from about 0.01% to about 85% by weight. In otherembodiments, the weighting agent may be present in the treatment fluidsof the present invention in the range from about 15% to about 70% byweight. One of ordinary skill in the art, with the benefit of thisdisclosure, will recognize the appropriate amount of weighting agent touse for a chosen application.

Optionally, other additives may be added to the treatment fluids of thepresent invention as deemed appropriate by one skilled in the art withthe benefit of this disclosure. Examples of such additives include,inter alia, defoamers, curing agents, salts, corrosion inhibitors, scaleinhibitors, and formation conditioning agents. One of ordinary skill inthe art with the benefit of this disclosure will recognize theappropriate type of additive for a particular application.

Certain embodiments of the fluids of the present invention maydemonstrate improved “300/3” ratios. As referred to herein, the term“300/3” ratio will be understood to mean the value that results fromdividing the shear stress that a fluid demonstrates at 300 rpm by theshear stress that the same fluid demonstrates at 3 rpm. When treatmentfluids are used as spacer fluids, an ideal “300/3” ratio would closelyapproximate 1.0, indicating that the rheology of such fluid is flat.Flat rheology will facilitate, inter alia, maintenance of nearly uniformfluid velocities across a subterranean annulus, and also may result in anear-constant shear stress profile. In certain embodiments, flatrheology may reduce the volume of a spacer fluid that is required toeffectively clean a subterranean well bore. Certain embodiments of thefluids of the present invention may demonstrate 300/3 ratios in therange of from about 2.7 to about 4.2. Certain embodiments of the fluidsof the present invention may maintain a nearly flat rheology across awide temperature range.

The fluids of the present invention may be prepared in a variety ofways. In certain embodiments of the present invention, the well fluidsof the present invention may be prepared by first pre-blending thevitrified shale with certain optional dry additives. Next, the blendeddry materials may be mixed with base fluid in the field, either by batchmixing or continuous (“on-the-fly”) mixing. In certain embodiments ofthe present invention wherein the blended dry materials are mixed withbase fluid by batch mixing, a weak organic acid and defoamers typicallywill be premixed into the base fluid. The dry blend then may be added tothe base fluid using, e.g., an additive hopper with venturi effects; themixture of the dry blend and the base fluid also may be agitated, afterwhich the weighting material may be added and agitated. Surfactants maybe added to the spacer fluid shortly before it is placed down hole. Incertain embodiments of the present invention wherein the blended drymaterials are mixed with base fluid by continuous mixing, the blendeddry materials typically will be further blended with a weightingmaterial, and the resulting mixture may be metered into, e.g.,recirculating cement mixing equipment while the base fluid is metered inseparately. The base fluid typically will comprise defoamers pre-blendedtherein. Shortly before the spacer fluid is placed down hole,surfactants may be added to the spacer fluid.

An example of a method of the present invention is a method ofdisplacing a fluid in a well bore, comprising: providing a well borehaving a first fluid disposed therein; and placing a second fluid intothe well bore to at least partially displace the first fluid therefrom,wherein the second fluid comprises vitrified shale and a base fluid.

Another example of a method of the present invention is a method ofseparating fluids in a well bore in a subterranean formation,comprising: providing a well bore having a first fluid disposed therein;placing a spacer fluid in the well bore to separate the first fluid froma second fluid, the spacer fluid comprising a vitrified shale and a basefluid; and placing a second fluid in the well bore.

An example of a composition of the present invention comprises 51.39%water by weight, 3.19% vitrified shale by weight, 43.81% barite byweight, 0.94% sepiolite by weight, 0.034% hydroxyethyl cellulose byweight, 0.08% BIOZAN by weight, 0.006% modified sodium lignosulfonate byweight, and 0.55% citric acid by weight.

To facilitate a better understanding of the present invention, thefollowing examples of preferred embodiments are given. In no way shouldthe following examples be read to limit, or to define, the scope of theinvention.

EXAMPLE 1

Rheological testing was performed on a variety of sample compositionsthat were prepared as follows. First, all dry components (e.g.,vitrified shale, or zeolite, or fumed silica, plus dry additives suchas, for example, hydroxyethylcellulose, BIOZAN, and sodiumlignosulfonate were weighed into a glass container having a clean lid,and thoroughly agitated by hand until well blended. Tap water then wasweighed into a Waring blender jar, and the blender turned on at 4,000rpm. While the blender continued to turn, citric acid was added to themixing water, and then the blended dry components were added, followedby the barite. The blender speed then was increased to 12,000 rpm forabout 35 seconds. Afterwards, the blender was stopped, and about 2 dropsof a standard, glycol-based defoamer were added.

Rheological values then were determined using a Fann Model 35viscometer. Dial readings were recorded at speeds of 3, 6, 30, 60, 100,200, 300, and 600 RPM with a B1 bob, an R1 rotor, and a 1.0 spring.

In the Sample Compositions described below, all concentrations are inweight percent.

Sample Composition No. 1 comprised a 10 pound per gallon slurry of 75.6%water, 4.83% zeolite, 1.63% sepiolite, 0.04% hydroxyethylcellulose,0.11% BIOZAN, 0.71% sulfonated styrene copolymer, 0.72% citric acid, and16.36% barite.

Sample Composition No. 2 comprised a 10 pound per gallon slurry of 75.6%water, 4.83% fumed silica, 1.63% sepiolite, 0.04% hydroxyethylcellulose,0.11% BIOZAN, 0.71% sulfonated styrene copolymer, 0.72% citric acid, and16.36% barite.

Sample Composition No. 3 comprised a 10 pound per gallon slurry of 75.6%water, 5.49% vitrified shale, 1.61% sepiolite, 0.07%hydroxyethylcellulose, 0.14% BIOZAN, 0.01% modified sodiumlignosulfonate, 0.72% citric acid, and 16.36% barite.

Sample Composition No. 4 comprised a 13 pound per gallon slurry of51.39% water, 2.81% zeolite, 0.95% sepiolite, 0.02%hydroxyethylcellulose, 0.06% BIOZAN, 0.41% sulfonated styrene copolymer,0.55% citric acid, and 43.81% barite.

Sample Composition No. 5 comprised a 13 pound per gallon slurry of51.39% water, 2.81% fumed silica, 0.95% sepiolite, 0.02%hydroxyethylcellulose, 0.06% BIOZAN, 0.41% sulfonated styrene copolymer,0.55% citric acid, and 43.81% barite.

Sample Composition No. 6 comprised a 13 pound per gallon slurry of51.39% water, 3.19% vitrified shale, 0.94% sepiolite, 0.034%hydroxyethylcellulose, 0.08% BIOZAN, 0.006% modified sodiumlignosulfonate, 0.55% citric acid, and 43.81% barite.

Sample Composition No. 7 comprised a 16 pound per gallon slurry of36.22% water, 1.54% zeolite, 0.52% sepiolite, 0.01%hydroxyethylcellulose, 0.04% BIOZAN, 0.23% sulfonated styrene copolymer,0.45% citric acid, and 60.98% barite.

Sample Composition No. 8 comprised a 16 pound per gallon slurry of36.22% water, 1.54% fumed silica, 0.52% sepiolite, 0.01%hydroxyethylcellulose, 0.04% BIOZAN, 0.23% sulfonated styrene copolymer,0.45% citric acid, and 60.98% barite.

Sample Composition No. 9 comprised a 16 pound per gallon slurry of36.22% water, 1.76% vitrified shale, 0.52% sepiolite, 0.023%hydroxyethylcellulose, 0.044% BIOZAN, 0.003% modified sodiumlignosulfonate, 0.45% citric acid, and 60.98% barite.

The results of the testing are set forth in the tables below. Theabbreviation “PV” stands for plastic viscosity , while the abbreviation“YP” refers to yield point. TABLE 2 Sample Viscometer RPM CompositionTemp. 600 300 200 100 60 30 6 3 PV YP 1  80 F. 43 30 25 19 15 12 7 619.5 11.9 1 135 F. 35 26 21 16 13 11 7 5 16.4 10.5 1 190 F. 31 23 20 1614 12 9 8 12 12.2 2  80 F. 40 27 23 19 16 14 9 7 14.1 14.2 2 135 F. 3224 21 18 15 12.5 9 8 12.1 13.4 2 190 F. 29 21 18 15 13 12 9 7.5 9.9 11.93  80 F. 49 35 29 21 17 13 8 7 18.0 15.0 3 135 F. 49 36 30 23 19 16 10 917 18 3 190 F. 39 29 24 18 15 12 8 7 14 14

TABLE 3 Sample Viscometer RPM Composition Temp. 600 300 200 100 60 30 63 PV YP 4  80 F. 102 72 59 43 35 28 17 15 48.1 26.8 4 135 F. 77 55 46 3630 25 16 14 32.5 24.9 4 190 F. 55 40 33 25 21 17 11 10 24.9 16.7 5  80F. 89 63 51 37 30 23 14 12 43.3 22.2 5 135 F. 63 46 38 29 24 19 12 11 2919 5 190 F. 45 34 27 20 18 15 10 8 20.6 14.1 6  80 F. 84 59 49 37 32 2416 14 30.0 28.0 6 135 F. 65 46 38 28 23 18 12 10 24 20 6 190 F. 51 37 3124 20 17 11 10 18 19

TABLE 4 Sample Viscometer RPM Composition Temp. 600 300 200 100 60 30 63 PV YP 7  80 F. 172 123 101 75 62 50 36 31 79.5 48.5 7 135 F. 127 92 7758 49 41 28 26 56 40 7 190 F. 105 76 65 51 45 37 27 23 41.9 37.8 8  80F. 177 127 105 79 65 52 37 34 81.3 51.2 8 135 F. 114 82 69 53 46 39 2825 47 38.4 8 190 F. 95 69 57 44 37 31 22 20 41.2 30.4 9  80 F. 109 82 6952 44 36 26 23 38.0 40.0 9 135 F. 92 67 56 44 37 31 23 21 31 34 9 190 F.75 56 48 39 34 29 22 21 23 32

The above Example demonstrates, inter alia, that the improved treatmentfluids of the present invention comprising vitrified shale and a basefluid may be suitable for use in treating subterranean formations.

EXAMPLE 2

Additional Theological testing was carried out on several fluids havingthe following compositions.

Sample Composition No. 10, a well fluid of the present invention,comprised 60.98% fresh water by weight, 1.76% vitrified shale by weight,36.22% barium sulfate by weight, 0.52% sepiolite by weight, 0.023%hydroxyethyl cellulose by weight, 0.044% BIOZAN by weight, 0.003%modified sodium lignosulfonate by weight, and 0.45% citric acid byweight.

Sample Composition No. 11 comprised 0.97% bentonite by weight, 27.79%silica flour by weight, 0.2% carboxymethyl hydroxyethyl cellulose byweight, 40.04% barium sulfate by weight, 0.37% by weight of sodiumnapthalene sulfonate condensed with formaldehyde, and 31.63% fresh waterby weight.

Sample Composition No. 12 comprised 2.03% diatomaceous earth by weight,1.82% coarse silica by weight, 0.1% attapulgite by weight, 0.63%sepiolite by weight, 0.52% by weight of sodium napthalene sulfonatecondensed with formaldehyde, 0.1% propylene glycol by weight, 59.1%barium sulfate by weight, and 35.7% fresh water by weight.

The compositions were tested to determine their “300/3” ratios. Aviscometer using an R-1 rotor, a B-1 bob, and an F-1 spring was used.The dial readings at 300 RPM (511 sec⁻¹ of shear) were divided by dialreadings obtained at 3 RPM (5.11 sec⁻¹ of shear). The results of thetesting are set forth in the table below. TABLE 5 Sample Sample SampleComposition Composition Composition Rheology No. 10 No. 11 No. 12 300/3ratio at 80° F. 4.2 11.0 9.0 300/3 ratio at 135° F. 2.7 7.8 5.8 300/3ratio at 190° F. 3.0 5.3 5.6

Therefore, the present invention is well adapted to carry out theobjects and attain the ends and advantages mentioned as well as thosewhich are inherent therein. While the invention has been depicted anddescribed by reference to exemplary embodiments of the invention, such areference does not imply a limitation on the invention, and no suchlimitation is to be inferred. The invention is capable of considerablemodification, alternation, and equivalents in form and function, as willoccur to those ordinarily skilled in the pertinent arts and having thebenefit of this disclosure. The depicted and described embodiments ofthe invention are exemplary only, and are not exhaustive of the scope ofthe invention. Consequently, the invention is intended to be limitedonly by the spirit and scope of the appended claims, giving fullcognizance to equivalents in all respects.

1. A spacer fluid comprising a vitrified shale and a base fluid, whereinthe spacer fluid is not settable.
 2. The spacer fluid of claim 1 whereinthe vitrified shale comprises any partially vitrified silica-richmaterial.
 3. The spacer fluid of claim 1 wherein the vitrified shale ispresent in the spacer fluid an amount in the range of from about 0.01%to about 90% by weight of the spacer fluid.
 4. The spacer fluid of claim1 wherein the vitrified shale is present in an amount in the range offrom about 1% to about 10% by weight of the spacer fluid.
 5. The spacerfluid of claim 1 wherein the base fluid comprises at least one basefluid selected from the group consisting of: an aqueous-based fluid, anemulsion, a synthetic fluid, and an oil-based fluid.
 6. The spacer fluidof claim 1 wherein the base fluid is present in the spacer fluid in anamount sufficient to form a pumpable slurry.
 7. The spacer fluid ofclaim 1 further comprising a viscosifying agent.
 8. The spacer fluid ofclaim 8 wherein the viscosifying agent comprises at least oneviscosifying agent selected from the group consisting of: a colloidalagent, an emulsion forming agent, a diatomaceous earth, a starch, and amixture thereof.
 9. The spacer fluid of claim 9 wherein the viscosifyingagent comprises at least one colloidal agent selected from the groupconsisting of: a clay, a polymer, a guar gum, and a mixture thereof. 10.The spacer fluid of claim 10 wherein the viscosifying agent comprises atleast one clay selected from the group consisting of: kaolinite,montmorillonite, bentonite, a hydrous mica, attapulgite, sepiolite,laponite, and a mixture thereof.
 11. The spacer fluid of claim 8 whereinthe viscosifying agent is present in the spacer fluid in an amount inthe range of from about 0.05% to about 10% by weight of the spacerfluid.
 12. The spacer fluid of claim 1 wherein the spacer fluid furthercomprises at least one of the following: a dispersant, a surfactant, aweighting agent, a fluid loss control additive, or a mixture thereof.13. The spacer fluid of claim 14 wherein the spacer fluid comprises atleast one dispersant selected from the group consisting of: a sulfonatedstyrene maleic anhydride copolymer, a sulfonated vinyltoluene maleicanhydride copolymer, a sodium naphthalene sulfonate condensed withformaldehyde, a sulfonated acetone condensed with formaldehyde, alignosulfonate, an allyloxybenzene sulfonate, an allyl sulfonate, anon-ionic monomer, an interpolymer of acrylic acid, and a mixturethereof.
 14. The spacer fluid of claim 15 wherein the dispersant ispresent in the spacer fluid in an amount in the range of from about0.0001% to about 4% by weight of the spacer fluid.
 15. The spacer fluidof claim 14 wherein the spacer fluid comprises at least surfactantselected from the group consisting of: a nonylphenol ethoxylate, analcohol ethoxylate, a sugar lipid, an α-olefinsulfonate, analkylpolyglycoside, an alcohol sulfate, a salt of ethoxylated alcoholsulfate, an alkyl amidopropyl dimethylamine oxide, an alkene amidopropyldimethylamine oxide, and a mixture thereof.
 16. The spacer fluid ofclaim 17 wherein the surfactant is present in the spacer fluid in anamount in the range from about 0.01% to about 10% by weight of thespacer fluid.
 17. The spacer fluid of claim 14 wherein the spacer fluidcomprises at least one weighting agent selected from the groupconsisting of: barite, hematite, manganese tetraoxide, ilmenite, calciumcarbonate, and a mixture thereof.
 18. A spacer fluid comprising: avitrified shale in an amount in the range of from about 1% to about 10%by weight of the spacer fluid, and a base fluid, wherein the spacerfluid is not settable.
 19. The spacer fluid of claim 18 wherein thevitrified shale comprises any partially vitrified silica-rich material.20. The spacer fluid of claim 18 wherein the spacer fluid furthercomprises at least one of the following: a dispersant, a surfactant, aweighting agent, a fluid loss control additive, or a mixture thereof.